The present invention relates to a multi-vehicle arrangement for heavy haulage comprising at least a first tractor unit mechanically connected with a second tractor unit.
Heavy haulage relates to road transport of abnormal loads. This is normally performed by means of a tractor unit and a customised trailer adapted for the abnormal load. The load can for example be abnormal in weight and/or in size. One prior art solution for transporting even larger loads is given in US 2001/0003393, where a multi-combination vehicle comprising a prime mover including a first power source arranged in the prime mover, and a trailer mechanically coupled to the prime mover and including a second power source arranged in the trailer. The increased power provided from the second power source results in improved power-to-weight ratio of the vehicle.
One specific problem with the solution according to the prior art is that the carrier must be specifically designed, and subsequently manufactured in a very low number of units due the limited demand of such a highly specialised device, leading to high costs of the overall vehicle arrangement.
There is thus a need for an improved vehicle arrangement for heavy haulage purposes that removes the above mentioned disadvantage.
It is desirable to provide an inventive multi-vehicle arrangement for heavy haulage, where the previously mentioned problems are partly avoided. According to an aspect of the present invention, each tractor unit forms a separately drivable tractor unit comprising a driver cab, a digital communication device, steering wheels, a braking system, and a power train comprising a power source, a friction clutch, and an automatic transmission, where said friction clutch is arranged to be disengaged or engaged for drive torque transmission from said power source to said automatic transmission, a digital communication link is provided between said tractor units by means of said digital communication devices, and a control system of said first tractor unit is arranged to control at least a clutch load of said friction clutch of each of said first and second tractor units for the purpose of reducing the risk of overheating of any of said friction clutches during engagement or disengagement of said friction clutches.
According to an aspect of the present invention, a method includes the steps of providing each tractor unit as a separately drivable tractor unit comprising at least a driver cab, a digital communication device, steering wheels, a braking system, and a power train comprising a power source, a friction clutch, and an automatic transmission, where said friction clutch is arranged to be disengaged or engaged for drive torque transmission from said power source to said automatic transmission. Further providing a digital communication link between said tractor units by means of said digital communication devices, and controlling at least a clutch load of said friction clutch of each of said first and second tractor units by means of a control system of said first tractor unit for the purpose of reducing the risk of over-heating of any of said friction clutches during engagement or disengagement of said friction clutches.
By forming the multi-vehicle arrangement from at least two separately drivable tractor units, no expensive specially designed trailer must be manufactured. Instead, two standard tractor units that otherwise are used separately can be combined for performing a special heavy haulage assignment, thus increasing total heavy haulage capacity. The standard tractor units to be connected may be of different types and/or or having different power train specifications. Consequently, heavy haulage assignments can be conducted more flexible, without the use of an expensive special trailer required on the desired location.
Tractor units for heavy haulage are frequently equipped with torque converter transmissions because of their capability of relatively large levels of transmission slip without excessive wear or overheating of the transmission. Torque converter transmissions however due to their inherent design have relatively large friction losses those results in increased fuel consumption. Automatic transmissions based on friction clutches have relatively low friction losses, and consequently also low fuel consumption, but there is an increased risk of overheating of the friction clutch instead, in particular dry friction clutches.
During vehicle start from a still stand state to a rolling state in a friction clutch based heavy haulage arrangement, the friction clutch of each tractor unit will during engagement thereof initially slip until the speed of the heavy haulage arrangement is sufficient to have equal rotation speed of the friction clutch input and output shafts. Taking into account the abnormal loads of the heavy haulage arrangement, and potential road inclination, the friction clutch of each tractor unit experiences severe load, and the risk of overheating of the friction clutch is thus high. In case of multi-vehicle arrangement having at least two separately drivable tractor units, this risk is also high due to lack of synchronisation of the clutch load of each tractor unit. The front tractor unit may for example operate on maximal power, whereas the following tractor unit only operates on 50% of full power. This situation quickly results in damages to the friction clutch of the front tractor unit. A similar situation may of course occur during disengagement of the friction clutches.
For the purpose of preventing overload of the friction clutch of any of the tractor units according to the invention, the control system of the first tractor unit is arranged to control the clutch load of said friction clutches for the purpose of reducing the risk of over-heating of any of said friction clutches of said first and second tractor units during engagement or disengagement of said friction clutches.
The control system may be arranged to control said friction clutch of each of said tractor units such that a relative clutch load of each friction clutch does not differ more than a certain amount.
The control system may further be arranged to at least between phases of gear shifts synchronise a relative drive torque of each of said tractor units.
The control system may further be arranged to control transmission mode of said automatic transmission of each of said tractor units.
The control system may further be arranged to control the braking system of each of said tractor units, for the purpose of equalising the braking load of each of said tractor units.
The control system may further be arranged to execute asynchronous gear shift of said automatic transmission of each of said tractor units, such that at least one tractor unit propels the multi-vehicle arrangement during gear shift phases of another tractor unit.
The multi-vehicle arrangement may operate in a master/slave configuration, wherein said second tractor unit is slaved to the control output of the control system of the first tractor unit.
The control system of said first tractor unit may further be arranged to control at least a clutch energy level of said friction clutch of each of said first and second tractor units by means of taking into account also clutch slipping time of each friction clutch for the purpose of reducing the risk of over-heating of any of said friction clutches.
The control system preferably takes into account individual friction clutch upper limit energy level of each of said friction clutches when controlling said clutch load of each friction clutch.
The control system preferably takes into account an individual power dissipation rate of each friction clutch when controlling said clutch load of each friction clutch.
Steering direction, torque request and deceleration request of said first tractor unit are adapted to be provided by a driver of said first tractor unit, and steering direction and preferably also hand brake of said second tractor unit are adapted to be provided by a driver of said second tractor unit.